Method, apparatus, and article for force feedback based on tension control and tracking through cables

ABSTRACT

A haptic device for human/computer interface includes a user interface tool coupled via cables to first, second, third, and fourth cable control units, each positioned at a vertex of a tetrahedron. Each of the cable control units includes a spool and an encoder configured to provide a signal corresponding to rotation of the respective spool. The cables are wound onto the spool of a respective one of the cable control units. The encoders provide signals corresponding to rotation of the respective spools to track the length of each cable. As the cables wind onto the spools, variations in spool diameter are compensated for. The absolute length of each cable is determined during initialization by retracting each cable In turn to a zero length position. A sensor array coupled to the tool detects rotation around one or more axes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.10/811,310, filed Mar. 26, 2004, now pending, which claims benefit,under 35 U.S.C. §119(e), of U.S. Provisional Patent Application No.60/458,171, filed Mar. 26, 2003, both of which are incorporated herein,by reference, in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The disclosure is generally related to haptic systems employing forcefeedback.

2. Description of the Related Art

Touch, or haptic interaction is a fundamental way in which peopleperceive and effect change in the world around them. Our veryunderstanding of the physics and geometry of the world begins bytouching and physically interacting with objects in our environment. Thehuman hand is a versatile organ that is able to press, grasp, squeeze orstroke objects; it can explore object properties such as surfacetexture, shape and softness; and it can manipulate tools such as a penor wrench. Moreover, touch interaction differs fundamentally from allother sensory modalities in that it is intrinsically bilateral. Weexchange energy between the physical world and ourselves as we push onit and it pushes back. Our ability to paint, sculpt and play musicalinstruments, among other things depends on physically performing thetask and learning from the interactions.

Haptics is a recent enhancement to virtual environments allowing usersto “touch” and feel the simulated objects with which they interact.Haptics is the science of touch. The word derives from the Greekhaptikos meaning “being able to come into contact with”. The study ofhaptics emerged from advances in virtual reality. Virtual reality is aform of human-computer interaction (as opposed to keyboard, mouse andmonitor) providing a virtual environment that one can explore throughdirect interaction with our senses. To be able to interact with anenvironment, there must be feedback. For example, the user should beable to touch a virtual object and feel a response from it. This type offeedback is called haptic feedback.

In human-computer interaction, haptic feedback refers both to tactileand force feedback. Tactile, or touch feedback is the term applied tosensations felt by the skin. Tactile feedback allows users to feelthings such as the texture of virtual surfaces, temperature andvibration. Force feedback reproduces directional forces that can resultfrom solid boundaries, the weight of grasped virtual objects, mechanicalcompliance of an object and inertia.

Tactile feedback, as a component of virtual reality simulations, waspioneered at MIT. In 1990 Patrick used voice coils to provide vibrationsat the fingertips of a user wearing a Dextrous Hand Master Exoskeleton.Minsky and her colleagues developed the “Sandpaper” tactile joystickthat mapped image texels to vibrations (1990). Commercial tactilefeedback interfaces followed, namely the “Touch Master” in 1993, theCyberTouch® glove in 1995, and more recently, the “FEELit Mouse” in1997.

Scientists have been conducting research on haptics for decades. Goertzat Argonne National Laboratories first used force feedback in a robotictele-operation system for nuclear environments in 1954. Subsequently thegroup led by Brooks at the University of North Carolina at Chapel Hilladapted the same electromechanical arm to provide force feedback duringvirtual molecular docking (1990). Burdea and colleagues at RutgersUniversity developed a light and portable force feedback glove calledthe “Rutgers Master” in 1992. Commercial force feedback devices havesubsequently appeared, such as the PHANTOM™ arm in 1993, the ImpulseEngine in 1995 and the CyberGrasp® glove in 1998.

Haptic devices (or haptic interfaces) are mechanical devices thatmediate communication between the user and the computer. Haptic devicesallow users to touch, feel and manipulate three-dimensional objects invirtual environments and tele-operated systems. Most common computerinterface devices, such as basic mice and joysticks, are input-onlydevices, meaning that they track a user's physical manipulations butprovide no manual feedback. As a result, information flows in only onedirection, from the peripheral to the computer. Haptic devices areinput-output devices, meaning that they track a user's physicalmanipulations (input) and provide realistic touch sensations coordinatedwith on-screen events (output). Examples of haptic devices includeconsumer peripheral devices equipped with special motors and sensors(e.g., force feedback joysticks and steering wheels) and moresophisticated devices designed for industrial, medical or scientificapplications (e.g., PHANTOM™ device).

Haptic interfaces are relatively sophisticated devices. As a usermanipulates the end effecter, grip or handle on a haptic device, encoderoutput is transmitted to an interface controller at very high rates.Here the information is processed to determine the position of the endeffecter. The position is then sent to the host computer running asupporting software application. If the supporting software determinesthat a reaction force is required, the host computer sends feedbackforces to the device. Actuators (motors within the device) apply theseforces based on mathematical models that simulate the desiredsensations. For example, when simulating the feel of a rigid wall with aforce feedback joystick, motors within the joystick apply forces thatsimulate the feel of encountering the wall. As the user moves thejoystick to penetrate the wall, the motors apply a force that resiststhe penetration. The farther the user penetrates the wall, the harderthe motors push back to force the joystick back to the wall surface. Theend result is a sensation that feels like a physical encounter with anobstacle.

The human sensorial characteristics impose much faster refresh rates forhaptic feedback than for visual feedback. Computer graphics has for manyyears contented itself with low scene refresh rates of 20 to 30frames/sec. In contrast, tactile sensors in the skin respond best tovibrations that are more than an order-of-magnitude higher than visualrates. This order-of-magnitude difference between haptics and visionbandwidths often requires that the haptic interface incorporate adedicated controller. Because it is computationally expensive to convertencoder data to end effecter position and translate motor torques intodirectional forces, a haptic device will often have its own dedicatedprocessor. This removes computation costs associated with haptics andthe host computer can dedicate its processing power to applicationrequirements, such as rendering high-level graphics.

General-purpose commercial haptic interfaces used today can beclassified as either ground-based devices (force reflecting joysticksand linkage-based devices) or body-based devices (gloves, suits,exoskeletal devices). The most popular design on the market is alinkage-based system, which consists of a robotic arm attached to a grip(usually a pen). A large variety of linkage based haptic devices havebeen patented (examples include U.S. Pat. Nos. 5,389,865; 5,576,727;5,577,981; 5,587,937; 5,709,219; 5,828,813; 6,281,651; 6,413,229;6,417,638). The arm tracks the position of the grip and is capable ofexerting a force on the tip of this grip. To meet the haptic demandsrequired to fool one's sense of touch, sophisticated hardware andsoftware are required to determine the proper joint angles and torquesnecessary to exert a single point of force on the tip of the pen. Notonly is it difficult to control force output because of the updatedemand, the mass of a robotic arm introduces inertial forces that mustbe accounted for.

An alternative to a linkage-based device is one that is tension-based.Instead of applying force through links, cables are connected a point ona “grip” in order to exert a vector force on that grip. Encoders can beused to determine the lengths of the connecting cables, which in turncan be used to establish position of the cable connection point on thegrip. Motors are used to create tension in the cables, which results inan applied force at the grip. There is only one commercial tension baseddevice available, through a Japanese company called Cyverse.

The SPIDAR-G is a 7 degree of freedom haptic device that allowstranslational, rotational and grip force. This design resulted from Dr.Seahak Kim's PhD work (Dr. Seahak Kim is currently an employee of MimicTechnologies, Inc.). References for much of Dr. Seahak Kim's work on theSPIDAR-G have been listed above.

Predating Dr. Seahak Kim's work on the SPIDAR-G, Japanese Patent No.2771010 and U.S. Pat. No. 5,305,429 were filed that describe a “3D inputdevice” as titled in the patent. This system consists of a supportmeans, display means and control means. The support means is a cubicframe. Attached to the frame are 4 encoders and magnetic switchescapable of preventing string movement over a set of pulleys. The pulleysconnect the tip of each encoder to strings that are wound through thepulleys. Each string continues out of the pulley to connect with aweight that generates passive tension in the string. The ON/OFF magneticswitches allow the strings to be clamped in place on command from thehost computer. The strings connect to the user's fingertip, which areconnected to the weights through the pulleys. The user moves his or herfingertip to manipulate a virtual object in virtual environment, whichis displayed through a monitor. As the user moves his or her fingertip,the length of the four strings change, and a computer calculates athree-dimensional position based on the number of pulses from theencoder, which indicate the change of string length between the pulleysand the user's finger. If the three-dimensional position of thefingertip is found to collide with a virtual object as determined by acontrolling host computer, then the ON/OFF magnetic switch is signaledto grasp and hold each string so that movement is resisted. Forces arenot rendered in a specific direction, but resistance in all directionsindicates that a user has contacted a virtual object. When the fingertipis forced outside the boundary of a virtual object, the magnetic switchis turned off to release the strings. The user is then able to move hisor her finger freely.

The “3 dimensional input device” introduced in U.S. Pat. No. 5,305,429is not capable of controlling or rendering directional forces. It istherefore not possible to render three-dimensional forces in the mannertypically associated with a haptic device. In other words, this deviceis not capable of simulating haptic effects such as the feel or contactwith a virtual three-dimensional surface.

The “3 dimensional input device” cannot render controlled vector forcesbecause of the following reasons, (i) it is impossible to display exactdirectional force, because the device can only grasp or release eachstring by ON/OFF magnetic switches and cannot impose an exact tension ineach string; (ii) there is no accounting for the changing force appliedby the weights attached to each string which provide a variable tensionas the velocity of the moving weight changes the tension; (iii) there isno accounting for extraneous forces resulting from friction between theframe, pulleys, ON/OFF magnetic switches and the strings; and (iv) thereis no initialization sequence described which is required fordetermining initial string lengths as need for determining stringorientations and finger position so that forces can be reflectedaccurately. In summary this is not a true force feedback device, butinstead is only a tracking mechanism with a single force effect(direction nonspecific drag). As an input device, the system also lacksa robust measurement method for determining the length of the strings,which results in substantial fingertip position measurement errors.There is also no means for measuring orientation of the finger (roll,pitch and yaw).

A system that combines virtual reality with exercise is described inU.S. Pat. No. 5,577,981. This system uses sets of three cables withretracting pulleys and encoders to determine the position of points on ahead mounted display. Using the lengths of the three cables, theposition of the point in space is found. Tracking three points on thehelmet (9 cables) allows head tracking of 6 degrees of freedom. Threecables attached to motor and encoders are also used to control themovement of a boom that rotates in one dimension through a vertical slitin a wall. The boom also has a servomotor at its end, about which theboom rotates. It is claimed that the force and direction of forceapplied by the boom can be controlled via the cables, servo motor andcomputer software, but no details are provided for how this isaccomplished.

Applications have been filed for patents in Japan and the US to supportthe SPIDAR-G (as discussed earlier). This apparatus was titled“three-dimensional input apparatus” and was filed under patent No.2001-282448 in Japan, and a US patent application has also beensubmitted: No. 20010038376. This device also consists of a supportmeans, display means and control means similar to that described in U.S.Pat. No. 5,305,429. However, this device uses “at least seven strings”to accommodate “at least six degrees of freedom” (actually the patentapplication only explains 7 degrees of freedom with 8 strings, but aclaim is made for 6 degrees of freedom with seven strings). Thementioned support means includes a cubic frame, where a motor andencoder are attached to at least seven locations on the frame. The tipof each encoder is connected to a spool on a motor, and this spool windsthe string. The encoder and motor are rotated simultaneously. The motorsare meant to create tension in the strings in place of the weights usedin the earlier patent. Instead of the string attaching to the usersfinger, the strings attach to a sphere shaped grip.

This grip has a mechanical structure that consists of two poles that arerotated based on the grasp force between the thumb and other fingers ofthe user. Two strings are connected to each of the four extremities ofthe two poles. If the user moves the tool to manipulate a virtual objectin a virtual environment, as displayed through a monitor, each stringlength is changed, and the computer is used to calculate a threedimensional position (translation, rotation and grasp information) basedon the number of pulses from the encoder, which is an indication of achange in string length. If contact is made with a virtual object, thecontrolling computer is used to calculate the tensions in the stringsthat are necessary to render force and torque at the grip.

The system described in Japanese patent 2001-282448 can thereforeactively display translation, rotation, and grasp force. As a result,the user is able to “touch” virtual objects through the display offorce. However, the above-mentioned “3 Dimensional interface device”requires at least seven strings to determine position and render force,even if rotation and grip forces are not being applied, and, while thedesign described above is adequate for displaying seven degrees of forcefeedback, there are severe limitations imposed if less than sevendegrees of force feedback are required.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the invention, an input/output haptic interface isprovided, to input the position of a tool(s) held by the user to acomputer by directly determining position and orientation of the tool ina three-dimensional space. Tracking may be accomplished over as many assix degrees of freedom.

In another aspect, a method is provided, for determining a tool positionthrough cable lengths with minimal error. Position of the tool may alsobe established with alternative tracking mechanisms such as throughinfrared, electromagnetic, gyro or acceleration sensors.

In another aspect, an input/output haptic interface is provided, torender forces to a point on a tool held by a user over two or threedimensions as signaled from software running on a host computer.Multiple sets of cables render vector forces to multiple points on atool. Alternatively, multiple sets of cables render vector forces topoints on multiple tools used in the same workspace.

In yet another aspect, a new calibration system is provided, formaintaining tool position accuracy with minimal user intervention, evenafter powering down and reactivation of the apparatus over multipleiterations.

In a further aspect, an input/output haptic interface provides a userwith the “touch” sensation generated as a result of interaction withvirtual environments, which could include force effects such as contactforce resulting from tool collision with rigid or deformable virtualsurfaces, the pull, push, weight or vibration of a virtual objectcontacting a tool(s), and/or viscous resistance and inertia experiencedas a tool moves through virtual fluid.

In still a further aspect, an interface relays position and forces datato and from a robot (or similar system). Control of the robot (orsimilar system) through the invention can be used to establishtelepresence.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not drawn to scale, and some of these elementsare arbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn, are notintended to convey any information regarding the actual shape of theparticular elements, and have been solely selected for ease ofrecognition in the drawings.

FIG. 1 is a block diagram that describes the components of the inventionand how they relate to each other.

FIG. 2 is a perspective view of one possible configuration of theinterface device which includes tool translation effecter components,cables and a supporting frame.

FIG. 3 is a perspective view of one possible configuration of a tooltranslation effecter device.

FIG. 4 is a perspective view of another possible configuration of a tooltranslation effecter device that uses an eyelet rather than a pulley andassociated parts.

FIG. 5 is a top view of the tool translation effecter device shown inFIG. 3.

FIG. 6 is a side view of the tool translation effecter device shown inFIG. 3.

FIG. 7 shows the grooves on the second pulley of the tool translationeffecter device that help evenly guide a winding cable.

FIG. 8 is a perspective view of another possible configuration of theinterface device, which includes tool translation effecter components,cables, a supporting frame, a port and a minimally invasive othoscope.

FIG. 9 shows a typical cycle of information/action flow as position of atool is detected and force is displayed at the tool.

FIG. 10 shows a generalized schematic for rendering force and tracking atool over two dimensions.

FIG. 11 shows a configuration of the invention that will allow forces tobe applied and controlled on a port, or trocar, over two dimensions in asystem that might be used for minimally invasive surgery simulation. Thesystem also allows for tracking the position of the point on the portwhere the cables connect.

DETAILED DESCRIPTION OF THE INVENTION

While the system described in Japanese patent 2001-282448, and outlinedin the background section of this document, provides significantadvantages over the previous art, there are still some problems thatremain unaddressed. For example, when calculating the length of eachstring, error is introduced because a changing spool diameter resultingfrom string wrapped over itself on the spool is not accounted for; thedevice calculates rotation based on the length change in eight strings,where a minor error in length variation of one string can substantiallyaffect accuracy (calculation algorithm is not robust about rotation);there is no initialization sequence provided, which is necessary fordetermining initial string length as required for determining position,orientation and grip, and minimizing associated error; the grip isconnected with eight strings, so workspace is limited if the user wishesto avoid tangling the strings; and there is no accounting for extraneousforces resulting from friction between the frame, pulleys, motors andstrings.

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of theinvention. However, one skilled in the art will understand that theinvention may be practiced without these details. In other instances,well-known structures associated with motors, motor controllers,computers, microprocessors, memories and the like have not been shown ordescribed in detail to avoid unnecessarily obscuring descriptions of theembodiments of the invention.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.”

The headings provided herein are for convenience only and do notinterpret the scope or meaning of the claimed invention.

FIG. 1 shows a tension based force feedback system 10 using cables,includes a number of devices or modules, such as: an interface module100 to detect translational and rotational signals concerning thetracking of a tool manipulated by the user; a control module 200 toconvert analog and pulse signals generated from the interface device 100to digital signals and to relay force signals to the mentioned interfacedevice 100; a calculation module 300 to control force feedback, tocalculate the position of a tool based on translation and rotationalmanipulation by the user, and to mathematically represent objects and/orenvironments that might interact with the tool; a display module 400 forthe user to perceive visual and/or audible information about the tool160 and objects and/or environments which are modeled in the calculationdevice 300; and a robotic module 500, which in those embodiments of theinvention that are so configured, receives control instructions from,and provides feedback signals to, the calculation module 300.

FIG. 2 shows one possible configuration of the interface device 100.This configuration of the interface device includes a frame 110, fourcable control units, or tool translation effecter devices 120, 130, 140,and 150, a tool 160, and a sensor array, or tool rotation detectiondevice 170.

Reference to the tool 160 may also be construed to refer to a connectionpoint to which the cables 11, 12, 13, and 14 are attached. According tosome embodiments of the invention, a separate tool, device, handle, orother implement is coupled to the tool 160.

The frame 110 in FIG. 2 represents one possible structure for supportingthe tool translation effecter devices 120, 130, 140, and 150 and theother components that are located within a three dimensional space. Theframe 110 can be constructed from a variety of materials, such as sheetmetal, trusses or rigid plastic, and can take the form of a wide varietyof geometries that partially enclose a three dimensional volume. Themain requirement of the frame is to provide rigid support of elementssuch as the detection devices 120, 130, 140, and 150. At the same timethe frame geometry should allow the user to freely manipulate the tool160 within a prescribed workspace, without excessive collision of thetool 160, or the user's hands, with the frame 110. In the embodimentillustrated in FIG. 2, the prescribed workspace is approximately cubicwith the volume partially enclosed by sides 111-119.

Each tool translation effecter device 120, 130, 140 and 150 ispositioned in three-dimensional space, and coupled at a correspondinganchor point to the frame 110. In the embodiment of FIG. 2, the tooltranslation effecter device 120 is positioned at the end of the upperright arm on the frame side 111, the tool translation effecter device130 is positioned at the end of the upper left arm on the frame side112, the tool translation effecter device 140 is positioned at the lowerfront of the frame in the center of side 115, and the tool translationeffecter device 150 is positioned at the lower back of the frame in thecenter of side 116. Tool translation effecter devices 120 and 130 arecentered in-between the tool translation effecter devices 140 and 150when viewed along the X-axis. Tool translation effecter devices 140 and150 are centered in-between the tool translation effecter device 120 and130 when viewed along the Y-axis. The tool translation effecter devices120, 130, 140 and 150 can be positioned in a variety of configurations,and are not limited to that illustrated by FIG. 2. The main objectivewhen placing the tool translation effecter devices 120, 130, 140 and 150is to maximize the volume enclosed by the devices 120, 130, 140, 150given the geometry of the frame 110.

FIGS. 3, 5 and 6 show detailed views of an illustrative one of the tooltranslation effecter devices 120, 130, 140, 150. While translationeffecter device 120 is described for the purpose of illustration, itwill be understood that, according to one embodiment of the invention,translation effecter devices 130, 140, and 150 are substantiallyidentical in structure and operation.

The illustrated tool translation effecter 120 includes a mounting system121, a pulley 122, a first bearing 123, a motor 124, an encoder 125, aspool 126, a cable 11, a second bearing 128, and a motor brake 129.

The four tool translation effecter devices 120, 130, 140 and 150 of FIG.2 are oriented so that spools 126 generally guide the cables 11, 12, 13and 14 toward the tool 160 with the objective of minimizing friction inthe cable run (i.e., path) to the tool 160.

The mounting system 121 of each tool translation effecter 120, 130, 140,150 provides a path that guides the cable 11 from the spool 126 to thepulley 122, while providing stability for the spool 126 and the pulley122, so that the center of the axis of each stays fixed in position whentension is applied to the cable 11. The mounting system 121 alsoprovides a structure to couple the respective tool translation effecterdevice 120, 130, 140, 150 to the frame 110. The mounting system 121 alsopositions the pulley 122 away from both the frame 110 and the spool 126in a manner that enables ideal use of tool workspace. The mountingsystem 121 may vary in size or geometry depending on workspacerequirements.

The mounting system 121 includes a link 121 a that is fixed to a bracket121 c. A rotary fulcrum 121 b is attached to link 121 a through asecondary bearing 128. The rotary fulcrum 121 b can rotate about an axisthat is perpendicular to the adjacent face of link 121 a. The secondarybearing between link 121 a and rotary fulcrum 121 b allows smoothrotation around an axis defined by hole 121 e of FIG. 5 as illustratedby arrow 121 f (see FIG. 6). The hole 121 e runs through the center ofthe rotary fulcrum 121 b, and the cable 11 passes through the hole 121e. The cable 11 is guided to the pulley 122 from the spool 126 throughthe hole 121 e. The pulley 122 is mounted to the rotary fulcrum throughbracket 121 d. The pulley 122 rotates around bearing 123 as illustratedby arrow 121 g (FIG. 6), which lies between bracket 121 d and the pulley122. In addition to its attachment to link 121 a, bracket 121 c isattached to the motor 124, the brake 129, and also to the frame 110.

Each motor 124 is typically a DC motor that displays minimal back drivefriction. The shaft of each motor 124 is drivingly coupled to a spool126, which is in turn coupled to a cable 11. When the motor 124 turnsthe respective pulley 126, the cable 11 wraps or unwraps around thepulley 126. Tension occurs in each cable 11, 12, 13 and 14 since thecables 11, 12, 13 and 14 pull at the tool 160 in opposing directions.The display tension to each cable 11, 12, 13 and 14 is based on thetorque applied by the motors 124 to the spool 126 as governed by thecontrol device 200. In order to reduce backlash, a gear is not used,however some embodiments may include a gear where suitable.

An encoder 125 is coupled to each motor 124 and converts the user'smanipulation as represented by rotation of the motor shaft intoelectrical pulses that are sent to the control device 200. Typically, anoptical encoder is used with a resolution of 1024 pulses per rotation ofthe motor shaft. However, a variety of optical encoders can be used thathave a wide range of resolutions. An encoder is therefore chosen basedon application requirements and price constraints. Determiningtranslational movement of the tool 160 can be calculated from the lengthof each cable 11, 12, 13 and 14, which is determined from encoder 124pulse signals. There is a mathematical relationship between cable lengthchange, diameter of the spool 126, and the pulses per rotation. Thespool 126 can be made of a variety of materials, such as aluminum,steel, rigid plastic or any other stiff material. The spool 126 may begrooved as shown in FIG. 7, allowing the cable to wrap evenly aboutspool 126, although such is not required.

FIG. 4 shows, according to an alternative embodiment, a cable controlunit 135, wherein the pulley 122, the first bearing 123, the secondbearing 128, and parts 121 a, 121 b and 121 d (shown in FIG. 3) areomitted. In the place of these components is a low friction eyelet 122that guides the cable 11 from the spool 126 through the mounting system121. The cable control unit 135 has fewer moving parts than the cablecontrol unit 120 described with reference to FIGS. 3, 5, and 6, but may,in some applications, introduce more drag to the associated cable 11.

The cables 11, 12, 13 and 14 connect between the spools 126 of the tooltranslation effecters to the tool 160. The cables 11, 12, 13 and 14 areideally made of a material that is substantially inelastic undertension, such as Dacron fishing line, but any string, wire or othercable that is flexible, durable and exhibits minimal stretch undertension can be used. The cables 11, 12, 13 and 14 connect to a point, orseries of points in close proximity, on the tool 160 or tool holder. Thetool 160 might be a stylus, pen, pliers, wrench, forceps, needle holder,scalpel, endoscope, arthroscope, minimally invasive surgical tool orother mechanical or medical tool. The tool could be free floating asillustrated in FIG. 2, or might move through a pivot point, such as theport 172 as illustrated in FIG. 8, or the port 174 of FIG. 11. Anyobject that can be connected to the cables 11, 12, 13 and 14, such thatthe cables 11, 12, 13 and 14 can apply vector forces to a point, orseries of points in close proximity, on the object through cabletension, may be considered the tool 160 as used herein. The cables 11,12, 13, 14, apply a vector force to the tool 160.

According to an embodiment of the invention, the tool 160 also carries asensor array 170 having one or more sensors, such as gyro sensors,acceleration sensors, infrared or electromagnetic sensors that can relaysignals to the control module 200. The purpose of these sensors is torelay information that can be used to determine tool orientation (roll,pitch and yaw) at the control module 200. Such sensors can also be usedto relay information about the tool translation in the x, y and/or zdirections in three dimensional space instead of, or in addition to, theencoders 124 to determine the cable 11, 12, 13, and 14 lengths. Suchsensors are commercially available from a wide variety of vendors andtake a wide variety of shapes and configurations, so the details ofthese sensors have not been illustrated in the figures. The wires and/orwireless transmitters/receivers for to transferring sensor signals fromthe sensor array 170 to the control module 200 are also not shown in thefigures, although in at least one embodiment the cables 11, 12, 13, 14may carry such signals.

As has been previously explained, according to some embodiments of theinvention the tool 160 comprises a connection point to which the cables11, 12, 13, and 14 are attached. A separate tool or device may then becoupled to the tool 160. Accordingly, the sensor array 170 may beconfigured to detect rotation of the separate tool, as it moves orrotates in one or more axes within the tool 160.

According to another embodiment, the tool 160 includes a vibratingelement attached, whose frequency and magnitude of vibration areregulated by the control module 200. The vibration element may be usedto create tactile effects. Vibration can also be used to simulatedifferent materials. For example, a dissipating vibration signal at ahigh frequency might be used when simulating contact with steel ascompared to a dissipating vibration signal at a lower frequency, whichcould be used when simulating contact with wood. Suitable vibratingelements are generally known, such as those employed in paging devicesand cellular phones, so will not be discussed in detail in the interestof brevity.

The control module 200 sends control signals to the motors 124 andreceives signals from the encoders 125 of each tool translation effecterdevice 120, 130, 140, 150. The control module 200 includes three primarycomponents; a motor controller 210, which controls tension in each cable11, 12, 13 and 14 via the motors 124 as directed by the calculationmodule 300; an encoder counter 220 that receives and counts pulsesignals from the encoders 125 and provides these counts to thecalculation module 300; and an A/D converter 230 that converts analogsignals transmitted from each tool translation effecter device 120, 130,140, 150 to digital signals that are relayed between the calculationmodule 300 and the control module 200.

The calculation module 300 consists of a local processor, memory storageand associated components on a printed circuit board for implementinglocal software control. The calculation module 300 may also include aremote computer, such as a conventional Pentium processor type orworkstation with conventional memory and storage means. The remotecomputer may transfer data to the local processor through connectionssuch as USB, serial, parallel, Ethernet, Firewire, SCSI, or any othermeans of transferring data at a high rate. The calculation module 300processes information via software control. The functions of thecalculation module 300 may be classified into five parts or functions:an object/environment representation function 310, a positioncalculation function 320, a collision detection function 330, a forcecontrol function 340, and an application recording function 350.

According to an embodiment of the invention, some or all of theprocessing tasks, including those described with reference to thecontrol device 200 and the calculation device 300, may be performed by aconventional system or workstation.

The object/environment representation function 310 manages and controlsmodeling information about virtual (or real) objects, the threedimensional environment, the tool 160, and determines the properinteraction between the objects, environment and the tool 160. Theobject/environment representation function 310 might also includeinformation about a robotic module 500, information sent from therobotic module 500, and/or how movement of the tool 160 effectsnavigation of the robotic module 500. The visual representation of theseobjects is relayed from the object/environment representation function310 to the display module 400. The position calculation function 320determines the position of the tool 160 by processing signals from thecontrol module 200 about translation and rotational movement of the tool160. The collision detection function 330 determines whether a collisionhas occurred between modeled objects and the tool 160. This might alsoinclude the indication of existing environmental effects such as viscousresistance and inertia experienced as a tool 160 moves through virtualfluid. When the system 10 is used to control a robot associated with therobotic module 500, collisions may be collected from the robot as itcollides with real objects. The force control function 340 is used tocalculate tension of each cable 11 that is appropriate for renderingreaction forces that take place at the tool 160. The summation of vectorforces in the cables 11, 12, 13 and 14 will equal the reaction force atthe tool 160. Such forces might be the result of reaction forcescollected by a robot as it interacts with real objects. The applicationrecord function 350 manages all other software interaction that takesplace in an application that utilizes the system 10.

The display module 400 displays manufactured virtual objects modeledthrough the calculation module 300. The display module 400 might also beused to convey visual information about real objects, such as in thecase of using the system 10 to control the robotic system 500 asitinteracts with real objects. The display module 400 is typicallyunderstood to be a conventional video monitor type and may be, forexample, NTSC, PAL, VGA, or SVGA. The display module may also consist ofa head mounted display or a video projection system. The display module400 may relay a 2D representation or a stereoscopic representation for3D projection. The display module 400 might be used, for example, tocollocate stereoscopic representations into the workspace of the system10. This could be accomplished by placing the face of a monitor betweensides 116 and 117 or the images could be projected through mirrorslocated at the back, bottom or top of the frame 110. Stereoscopic imagesmay also be relayed through a head mounted display. The display module400 may relay virtual environments where the entire environment can beclassified as a rendered graphical image. The display module 400 mayalso transmit augmented environments where graphical rendering isoverlaid onto video feeds or “see through” displays of realenvironments. The display module 400 could also transmit pure video ofreal environments, such as might be the case when the system 10 is usedto control a robot operating in a real environment.

In one embodiment the system 10 performs a variety of processes. Aprocess to establish the initial length of each cable 11, 12, 13, and 14is achieved through processing transmitted signals between thecalculation device 300 and each encoder counter device 220 and byutilizing a history of encoder pulse counts from each tool translationeffecter 120, 130, 140 and 150 as stored in the calculation device 300.The system 10 performs the process of relaying position and orientation(roll, pitch and yaw) information about the tool 160 to the calculationdevice 300 through optical encoders and/or sensors such as gyro sensors,acceleration sensors, infrared or electromagnetic tracking mechanismslocated in and/or around the tool 160. The system 10 performs theprocess of establishing the position and orientation (roll, pitch andyaw) of the tool 160 in three dimensional space at the calculationdevice 300. The system 10 performs the process of determining theposition and orientation of the tool 160 with the calculation device 300from the signals sent by the control device 200 and/or the tool 160 tothe calculation device 300.

The system 10 further performs the process of establishing in thecalculation device 300 a force response that is appropriate at the tool160 based on position and orientation of the tool 160 as it relates tovirtual or real objects defined at the calculation device 300. Thesystem 10 carries out the process of determining tension values in eachcable 11, 12, 13, and 14 that will deliver a force response to the tool160 as determined at the calculation device 300, and controlling tensionin each cable 11, 12, 13, and 14, by driving the motor 124 of each tooltranslation effecter devices 120, 130, 140, 150 based on the tensionvalues determined in the calculation device 300. Finally, the system 10performs the process of relaying visual and audible information to thedisplay device 400 from the calculation device 300 about the locationand orientation of the tool 160 and virtual or real objects that thetool 160 may be interacting with.

A typical cycle of information/action flow is shown in FIG. 9, however,there would likely be more acts or steps in the case of representing avery complex environment. The steps of FIG. 9 utilize the processesoutlined above.

A process for establishing the initial length of each cable 11, 12, 13,and 14 is described below. According to one embodiment of the invention,these lengths are determined before the position of the tool 160 iscalculated. Calibrating these lengths can include the following acts:

1) The point on the tool 160 where the cable 11 is attached is moved tothe pulley 122 of the tool translation effecter 120 located on the upperright arm of the frame side on side 111. At this calibration point (P₁),the length of cable 11 extending from the pulley 122 to the tool 160 isconsidered to be 0 cm. The counter value of the encoder 125 of the tooltranslation effecter 120 is then set to 0 by the calculation device 300while the tool 160 is in this position. The encoder counts of each tooltranslation effecter 120, 130, 140 and 150 are recorded at thisposition.

2) The point on the tool 160 where the cable 12 is attached is moved tothe pulley 122 of the tool translation effecter 130 located on the upperleft arm of the frame on side 112. At this calibration point (P₂), thelength of cable 12 extending from the pulley 122 to the tool 160 isconsidered to be 0 cm. The counter value of the encoder 125 of the tooltranslation effecter 130 is then set to 0 by the calculation device 300while the tool 160 is in this position. The encoder counts of each tooltranslation effecter 120, 130, 140 and 150 are recorded at thisposition.

3) The point on the tool 160 where the cable 13 is attached is moved tothe pulley 122 of the tool translation effecter 140 located on the lowerfront portion of the frame on side 115. At this calibration point (P₃),the length of cable 13 extending from the pulley 122 to the tool 160 isconsidered to be 0 cm. The counter value of the encoder 125 of the tooltranslation effecter 140 is then set to 0 by the calculation device 300while the tool 160 is in this position. The encoder counts of each tooltranslation effecter 120, 130, 140 and 150 are recorded at thisposition.

4) The point on the tool 160 where the cable 14 is attached is moved tothe pulley 122 of the tool translation effecter 150 located on the lowerback portion of the frame on side 116. At this calibration point (P₄),the length of cable 14 extending from the pulley 122 to the tool 160 isconsidered to be 0 cm. The counter value of the encoder 125 of the tooltranslation effecter 150 is then set to 0 by the calculation device 300while the tool 160 is in this position. The encoder counts of each tooltranslation effecter 120, 130, 140 and 150 are recorded at thisposition. 5) There is now a relationship between the number of encoderpulses and the change in distance between the tool 160 and the pulleys122 attached to the tool translation effecters 120, 130, 140 and 150.The method for determining cable length and the position of the toolwill be described later in this document. At this point, the recordedencoder counts are adjusted to account for the fact that some pulsecounts were recorded before the counter value was set to zero. Valuescounted before the encoder was set to zero are offset by the appropriateamount. Steps 1 through 5 can be repeated to calibrate the device if itis believed that tracking inaccuracies exist, but normally, steps 1though 5 are only required when powering up the system 10 for the firsttime with a new computer.

6) When powering down the system 10, the calculation device 300 firstsignals for the current to be removed from each spring actuated brake128 attached to the motor spool 126 of the tool translation effecters120, 130, 140 and 150. This prevents the motors 124 from spinning theirrespective spools 126. This also keeps the encoders 125 locked inposition. The calculation device 300 can then store the current pulsecount from all the encoders 125 before completely powering down thesystem.

7) The next time the system 10 is powered up, the encoder pulse countvalues are then restored to each encoder 125 based on the values storedby the calculation device 300. Current to the brakes 128 is thenre-established by the calculation device 300, which releases the hold onthe motor spools 126. The tracking of the lengths of cables 11, 12, 13,and 14 can then resume as it did before the system 10 was last powereddown.

The process to relay position, orientation and rotational information ofthe tool 160 to the calculation device 300 though optical encodersand/or sensors such as gyro sensors, acceleration sensors, infrared orelectromagnetic tracking mechanisms located in and/or around the tool160 will now be discussed. The optical encoders 125 of the tooltranslation effecter devices 120, 130, 140, 150 output analog signalsthat are transferred to an ND converter 230. These signals are thenconverted to digital signals that are relayed to the calculation device300 as encoder pulse counts. The digital signals are transferred to theposition calculation part 320 of the calculation device 300 by way ofthe encoder counter part 220. The encoder pulse counts are used todetermine the lengths of the cables 11, 12, 13 and 14.

The system 10 may employ a sensor array 170 having, for example, threegyro sensors or acceleration sensors to detect rotational movement ofthe tool 160. The sensor array 170 outputs analog signals depending onrotational acceleration or rotational degree of movement of the tool160. The analog signals reflect rotation over three degrees of freedom(roll, pitch and yaw). These signals are transferred to A/D converter230, which converts the signals to digital signals. The digital signalsare then transferred to the position calculation part 320 of thecalculation device 300 by way of the encoder counter part 220. Theorientation (roll, pitch and yaw) of the tool 160 is determined based onthe digital information received according to means specified by themanufacturer of the gyro sensors or acceleration sensors. Such sensorscan also be used to transfer translation information about the tool 160in a similar manner to that described above. Other sensors such asinfrared or electromagnetic tracking mechanisms could likewise be used.

The process for finding tool position and orientation based on thedigital information sent from the control device 200 to the calculationdevice 300 can be accomplished by a variety of means. In particular,there are various approaches to finding the tool position based on cablelength. Some of these options are discussed in the following.

One simple approach for finding the position of the tool 160 is based onsolving four equations that define cable length. These equations containonly three unknown variables, which are the tool's rectangularcoordinates, x, y, and z. Equations 1 through 4 define the length l_(n)of each cable 11, 12, 13, 14 (where n=11, 12, 13, 14), where x_(i),y_(i) and z_(i) define the positions of the calibration points P_(i)(where i=1,2,3,4) and x, y and z is the point where the cable 11, 12, 13and 14 attach to the tool 160.

l ₁₁=√{square root over ((x−x ₁)²+(y−y ₁)²+(z−z ₁)²)}{square root over((x−x ₁)²+(y−y ₁)²+(z−z ₁)²)}{square root over ((x−x ₁)²+(y−y ₁)²+(z−z₁)²)}(Eq. 1)

l ₁₂=√{square root over ((x−x ₂)²+(y−y ₂)²+(z−z ₂)²)}{square root over((x−x ₂)²+(y−y ₂)²+(z−z ₂)²)}{square root over ((x−x ₂)²+(y−y ₂)²+(z−z₂)²)}(Eq. 2)

l ₁₃=√{square root over ((x−x ₃)²+(y−y ₃)²+(z−z ₃)²)}{square root over((x−x ₃)²+(y−y ₃)²+(z−z ₃)²)}{square root over ((x−x ₃)²+(y−y ₃)²+(z−z₃)²)}(Eq. 3)

l ₁₄=√{square root over ((x−x ₄)²+(y−y ₄)²+(z−z ₄)²)}{square root over((x−x ₄)²+(y−y ₄)²+(z−z ₄)²)}{square root over ((x−x ₄)²+(y−y ₄)²+(z−z₄)²)}(Eq. 4)

Consider the origin of the coordinate system to be in the center of theframe 110 shown in FIG. 2. Consider sides 115, 116 and 117 to be oflength 2a. Consider sides 111 and 112 to be of length b and sides 113and 114 to be 2b. Also consider sides 118 and 119 to be of length 2c.

Equations 1 through 4 can be combined to determine a solution for thetool position (as defined by coordinates x, y and z) in terms of thelengths a, b and c.

$\begin{matrix}{x = \frac{l_{12}^{2} - l_{11}^{2}}{4a}} & \left( {{Eq}.\mspace{14mu} 5} \right) \\{y = \frac{l_{14}^{2} - l_{13}^{2}}{4b}} & \left( {{Eq}.\mspace{14mu} 6} \right) \\{z = \frac{l_{14}^{2} + l_{13}^{2} - l_{12}^{2} - l_{11}^{2} + {2a^{2}} - {2b^{2}}}{8c}} & \left( {{Eq}.\mspace{14mu} 7} \right)\end{matrix}$

Equation 5 can be found by squaring both sides of equations 1 and 2,subtracting equation 1 from equation 2, and then by isolating thevariable x. Equation 6 can be found by squaring both sides of equations3 and 4, subtracting equation 3 from equation 4, and then by isolatingthe variable y. Equation 7 can be found by squaring both sides ofequations 1-4, adding equations 3 and 4 and from this subtract equations1 and 2, and then by isolating the variable z. It should be noted thatonly three of equations 1-4 are necessary to solve for x, y, and z, butusing all four equations is a simpler approach. There are a variety ofalgebraic mathematical methods for solving for x, y and z givenequations 1, 2, 3 and 4 and the invention is not limited to the solvingmethod described above.

To briefly summarize another method for determining the lengths of cable11, 12, 13 and 14, the calibrations points P₁, P₂, P₃, P₄ discussedearlier form a tetrahedral volume, V. The position of the tool 160 wherethe cables 11, 12, 13 and 14 are attached can be used to divide thistetrahedron volume into four smaller tetrahedrons. If P is the cableconnection point to the tool 160, consider V₁ the volume formed by P,P₂, P₃ and P₄, V₂ the volume formed by P, P₁, P₃ and P₄, V₃ the volumeformed by P, P₁, P₂ and P₄, and V₄ the volume formed by P, P₁, P₂ andP₃. Since we know the side lengths of all of these tetrahedrons, we candetermine these volumes from the side lengths (for example using Pierodella Francesca's formula or Heron's formula) where the distance betweenthe calibration points and the tool 160 (in other words, the cablelengths) form the sides. It is then possible to use volume coordinatesand shape functions to find the tool position (Zienkiewicz) as shownbelow.

$\begin{matrix}{x = {{\frac{V_{1}}{V}x_{1}} + {\frac{V_{2}}{V}x_{2}} + {\frac{V_{3}}{V}x_{3}} + {\frac{V_{4}}{V}x_{4}}}} & \left( {{Eq}.\mspace{14mu} 8} \right) \\{y = {{\frac{V_{1}}{V}y_{1}} + {\frac{V_{2}}{V}y_{2}} + {\frac{V_{3}}{V}y_{3}} + {\frac{V_{4}}{V}y_{4}}}} & \left( {{Eq}.\mspace{14mu} 9} \right) \\{z = {{\frac{V_{1}}{V}z_{1}} + {\frac{V_{2}}{V}z_{2}} + {\frac{V_{3}}{V}z_{3}} + {\frac{V_{4}}{V}z_{4}}}} & \left( {{Eq}.\mspace{14mu} 10} \right)\end{matrix}$

The cable lengths described in equations 1-7 are determined through thenumber of encoder pulses that result from spinning the spool 126 of thetool translation effecter devices 120, 130, 140, 150. Assume an encodercount of c pulses, where C represents the number counts per one completemotor shaft revolution (also known as encoder resolution). Also assumethe spool 126 has a radius of rand that the groove separation 126 a isd. The calibration process described earlier insures that the pulsecount is zero when the cable length is zero. The pulse number increasesas the cable unwraps from spool 126 of a tool translation effecter 120.Therefore, the length of each cable can be determined from the number ofpulses based on equation 11, where the subscript i refers to thedifferent tool translation effecter devices 120, 130, 140, 150 and theirassociated cables 11, 12, 13 and 14.

$\begin{matrix}{l_{i} = {\frac{c_{i}}{C}\sqrt{\left( {2\Pi \; r} \right)^{2} + d^{2}}}} & \left( {{Eq}.\mspace{14mu} 11} \right)\end{matrix}$

The difficulty with relying completely on equation 11 is that it ispossible for a cable 11 to become miss wrapped so that it does notperfectly follow the grooves 126 a of the spool 126. The cable 11 mightalso end up wrapping on top of previously wrapped cable if the spool 126width and/or radius are not great enough. This can change variables rand d of equation 11, which will introduce error if not accounted for.To address this source of error, the method described below can beemployed.

L _(ij) =m _(ij) p _(ij) +n _(ij)   (Eq. 12)

Equation 12 relates cable length at the calibration positions P₁, P₂, P₃and P₄ to the recorded encoder pulses obtained during the calibrationprocess. The cable length, L_(ij) is known at every calibration positionP_(j), where i refers to each of the four cables and j refers to thedifferent calibration positions (where i=1 . . . 4, j=1 . . . 4 andi≠j). The number of encoder counts recorded at these lengths for thecables, p_(ij), was recorded during the calibration process forcalibration positions P₁, P₂, P₃ and P₄. Given the known lengths,L_(ij), of the cables at each calibration position and recorded pulsecounts, p_(ij), the linear curve of equation 12 can be fit to the dataand variables m_(ij) and n_(ij) can be solved. Methods, such as theleast mean squared method, could be used to fit this curve. n_(ij) willbe close to zero so long as the encoder counters are set to zero at thecalibration positions and the relationship between pulse count andlength is truly linear. Otherwise, a spline or non-linear curve fitmight be more appropriate for defining the relationship between cablelength and pulse count

The process defined above for finding a linear relationship betweenencoder counts and cable length could be adapted to include more (orless) calibration positions as described for the calibration process.The user simply moves the point on the tool 160 where the cables 11, 12,13 and 14 are attached to a specified calibration point. So long as thelengths of all the cables 11, 12, 13 and 14 are known at this point andthe encoder counts are recorded at this position, then this data can beused to find a curve fit. The more calibration points the more accuratethe curve fit will be.

It is also possible to use cable lengths as determined from alternativetool tracking mechanisms, such as infrared, electromagnetic, gyro oracceleration sensors. These sensors may or may not be fast enough torecord tool positions at haptic compatible rates. If such a trackingmechanism is considered accurate, but provides too slow of an update forhaptics, the tracking mechanisms might be used to continuously calibratea tracking system based on the encoders 126 of the tool translationeffecter devices 120, 130, 140, 150. The alternative tool trackingmechanisms would yield tool positions, which in turn can be used todetermine cable lengths. These lengths can be associated with encodercounter values. A sample of such data can be used to fit a curve, suchas that defined by equations 12, to find an updated relationship betweencable length and encoder pulses at any given time. This method wouldtherefore not require the user to move to any specific calibrationpositions. Note that n_(ij) of equation 12 does not have to be zero inthis case, if the encoder counters are not set to zero at thecalibration positions.

The process to establish in the calculation device 300 a force responsethat is appropriate at the tool 160 is normally determined according tothe software application utilizing the system 10 under discussion.Typically, an application uses the tool 160 position and orientationinformation to determine if a collision has occurred with virtualobjects. The force response can be rendered to simulate a wide range ofeffects. For example, a force response might simulate a collision of thetool 160 with a rigid or deformable virtual surface, the pull, push,weight or vibration of a virtual object contacting the tool 160, and/orviscous resistance and inertia experienced as a tool 160 moves throughvirtual fluid. Forces could also be derived from a robot touching realobjects where the robot measures the reaction forces upon collision. Theonly limitation is that the force response determined at the calculationdevice 300 must be representable as a single vector force in the x, yand z direction at the point(s) where the cables 11, 12, 13, 14 connectwith the tool 160. It is this vector force that the user will feel atthe tool 160. This vector force can be updated at a rate that isappropriate for the application.

The process for determining tension values in each cable 11, 12, 13, and14 that will deliver a force vector response to the tool 160 asdetermined by the calculation device 300 will now be discussed. Theforce control part 340 calculates tension using the following equation.

J=(Aτ−f)+α[τ]²

for

min[J]²

  (Eq. 13)

In equation 13, τ is the tension where τ=τ₁, τ₂, τ₃, τ₄] in the cables11, 12, 13 and 14, α is a coefficient that displays stability of force,J is the target function. Consider w_(i) (i=11,12,13,14) (R^(ε3x1)) aset of unit force vectors (in 3D) that are displayed along the directionof tension for each cable 11, 12, 13 and 14. A={w₁₁, w₁₂, w₁₃, w₁₄)(R^(ε3x4)) is a force matrix filled with the unit vector forces.f=(f_(x), f_(y), f_(z)) is the force vector that is to be displayed atthe tool 160. The force control 340 calculates positive tension values,which minimizes the target function, J (in other words, J should end upclose to zero). A good value to use for α is 0.1, but the teachingsherein are not limited to the use of this value. A variety of standardmathematical methods can be used to minimize the target function J andthus determine τ.

The process to control tension in each cable 11, 12, 13, and 14 isaccomplished by driving each motor 124, 134, 144 and 154 based ontension values determined in the calculation device 300. The forcecontrol part 340 of the control device 300 regulates motor torque bycontrolling the current sent to the motors 124. Each motor 124 appliestorque to the attached spool 126. The torque that accomplishes theappropriate tension in each cable 11 is dependent on the radius of thespool 126, which is accounted for by the force control part 340 of thecontrol device 300.

A wide variety of structures can be used to control the process thatrelays visual and audible information to the display device 400 from thecalculation device 300. Typically, the location and orientation of thetool 160 and virtual or real objects that the tool 160 may beinteracting with are displayed graphically. This allows the user to seehow he or she is effecting a virtual environment or a robot as the usermoves the tool 160. This information is displayed according to thesoftware application utilizing the system 10 under discussion and couldconstitute a vast range of possible formats. Audio output can also beutilized to display information resulting from tool 160 interaction withvirtual objects or real objects encountered through a robot.

There are a variety of configurations that the system 10 can employ thatrely on the same concepts outlined above. According to one embodiment ofthe invention, The system 10 includes a tool shaft 180 that passesthrough a port 172, and is coupled at one end to the tool or attachmentpoint 160. The cables 11, 12, 13 and 14 are attached to the point 160,which is coupled to the tool shaft 180, which in turn passes through theport 172 of interface device 20, as shown in FIG. 8. While the system 10applies translation forces in the x, y and z direction through cable 11tensions to the point 160, or a set of points 160 in close proximity, onthe tool shaft 180, the user will feel an insertion force (along withpitch and yaw). In FIG. 8, the insertion force is along the direction ofthe tool shaft 180 as confined by the port 172. Pitch and yaw are feltat the tool shaft handle with the pivot point at the port 172. Such aconfiguration is ideal to apply three degrees of freedom force feedbackto minimally invasive instruments used when simulating a surgicalprocedure.

More degrees of force feedback, such as rotation around the tool shaft180 and grip force at a handle of the tool shaft, can be added throughadditional motors independent of the cable system. For example, a motorin the tool shaft 180, or attached to the port 172, allows twistingforce feedback, and a motor in the handle of the tool shaft 180 adds asqueezing grip force. Such uses of motors to apply simple force feedbackover 1 degree of freedom may be used to augment the system 10.

It is common when working through a port 172 to define forces in termsof moment around the port rather than vector forces as applied to theend of the tool attachment point 160. In this case, equation 15 shouldbe adjusted to accommodate moment about the port 172 which can bedefined as M_(x) and M_(y), and an insertion force f_(l) which is avector force in the direction of the shaft of the tool 180.

$\begin{matrix}{{J = {\left( {{{TA}\; \tau} - M} \right) + {\alpha \lbrack\tau\rbrack}^{2}}}{for}\left. {\min \lbrack J\rbrack}^{2}\Rightarrow 0 \right.{and}{T = \begin{bmatrix}0 & L_{z} & L_{y} \\L_{z} & 0 & L_{x} \\v_{x} & v_{y} & v_{z}\end{bmatrix}}} & \left( {{Eq}.\mspace{14mu} 14} \right)\end{matrix}$

In equation 14, consider the port 172 to be located at coordinate(N_(x), N_(y), N_(z)) and L_(x)=x-N_(x), L_(y)=y-N_(y) and L_(z)=z-N_(z)where x, y and z can be found using equations 5, 6 and 7. v={v_(x),v_(y), v_(z)} is a unit vector that points from the port 172 axis origin(or the port pivot point) toward the point on the tool 160 where thecables 11, 12, 13, 14 are connected. M={M_(x), M_(y), f_(l)} are themoment and insertion force values prescribed by the user.

Embodiments of the invention are not limited to three degrees of forcefeedback freedom. In general, n degrees of force feedback can beaccomplished with n+1 cables or feedback devices. FIG. 10 shows theschematic of a simple two-degree of freedom force feedback system 30,according to another embodiment of the invention. The system 30 requiresthree cables 11, 12, 13 and three tool translation effecter devices 120,130 and 140. Equations 1, 2 and 3 define the length of the three cables11, 12 and 13. Assume that tool translation effecter device 120 lies atcoordinate (0, b, 0), tool translation effecter device 130 lies atcoordinate (−a, −b, 0) and tool translation effecter device 140 lies atcoordinate (a, −b, 0). Equations 1, 2 and 3 can be combined to isolatethe x and y position values of the tool 160.

$\begin{matrix}{x = \frac{l_{12}^{2} - l_{13}^{2}}{4a}} & \left( {{Eq}.\mspace{14mu} 17} \right) \\{y = {\frac{l_{12}^{2} + l_{13}^{2}}{8b} - \frac{l_{11}^{2} - a^{2}}{4b}}} & \left( {{Eq}.\mspace{14mu} 18} \right)\end{matrix}$

Equation 13 can be used, with two dimensional coefficientrepresentations, to find two degrees of freedom force feedback in the xand y direction for the configuration shown in FIG. 10. τ is the tensionwhere τ=[τ₁₁, τ₁₂, τ₁₃] in the cables 11, 12 and 13. Consider w_(i)(i=11,12,13) (R^(ε2x1)) a set of unit force vectors (in 2D) that aredisplayed along the direction of tension in each cable 11, 12 and 13 inthe x-y plane. A={w₁₁,w₁₂,w₁₃) (R^(ε2x3)) is a force matrix filled withthe unit vector forces that correspond to the cables 11, 12 and 13.f=(f_(x), f_(y)) is the 2D force vector that is to be displayed at thetool 160. It should be noted that a force along the z axis will bepresent if the tool 160 is moved outside of the x-y plane. This forcewill always pull the tool 160 back toward the x-y plane.

FIG. 11 shows an interface device 40, according to another embodiment ofthe invention. The port 174 is elongated, with an upper end fixed to apivot point 171, while the point defined in other embodiments as thetool or attachment point 160 is defined in this embodiment as the lowerend 165 of the port 174, which is free to move, within the constraintsimposed by the device 40. In this configuration, the cables are attachedto the lower end 165 of the port 174 rather than the tool 160. The port174 rotates freely around the port axis origin 171 (or port pivot point)while the tool 190 itself slides freely through the port 174.

When finding the cable tensions that will result in moment about theport 174, which can be defined as M_(x) and M_(y), a reduced version ofequation 14 can be used. This is because insertion of the tool 190 isnot being constrained, so the insertion force is essentially zero. T andM of equation 14 are simply redefined to reflect the two degrees offorce feedback problem, as shown below:

$T = \begin{bmatrix}0 & L_{z} & L_{y} \\L_{z} & 0 & L_{x}\end{bmatrix}$ and M = {M_(x), M_(y)}

In equation 14, τ is the tension where τ=[τ₁, τ₂, τ₃] in the cables 11,12 and 13, respectively. Consider w_(i) (i=11,12,13) (R^(ε3x1)) a set ofunit force vectors (in 3D) that are displayed along the direction oftension in each cable 11, 12 and 13. A={w₁₁, w₁₂, w₁₃) (R^(ε3x3)) is aforce matrix filled with the unit vector forces that correspond to thecables 11, 12 and 13.

It may be seen that when the port 174 is rotated on the pivot point 171,the cable connection point 165 of the port 174 moves out of the x-yplane, as shown in dotted lines in FIG. 11. Because f_(z) does existwhen the point 165 is moved out of the x-y plane, it is not straightforward to convert from moments about a port 174 to cable tensions usingequation 16. By accounting for the forces that result in the z directionas the cable connection point 165 on the port 174 moves out of the x-yplane when the port 174 is rotated, accurate moments (M={M_(x), M_(y)}),can be achieved.

While the x, y and z position on the port 174, where the cables 11, 12,13 attach, can be solved using only equations 1, 2 and 3, it is alsoconvenient to consider the constant length of the port shaft 15 as l₁₄.Under this assumption, equations 5, 6 and 7 can be used to determineposition. This is only one example of how to determine position for theconfiguration of FIG. 11. Methods similar to those discussed earlieralso apply.

Rotational feedback and gripping force feedback may also be provided forthe tool 190 of FIG. 10, as has been described in more detail withreference to the tool shaft 180 of FIG. 8.

Although not shown in any figure, a set of cables may be applied tomultiple points on a tool so that different vector forces can berendered at each point. A single calculation device can be used tocontrol all the cable sets, or different calculation devices, forexample on separate circuit boards, may be used. The effect of applyingseparate force vectors to different points on a single tool yields theeffect of rotational forces as felt by the user, or may serve to controlthe movement of a jointed tool. Multiple sets of cables can also be usedto apply force vectors to multiple tools that exist in the sameworkspace.

Although specific embodiments of and examples for the haptic system andmethod are described herein for illustrative purposes, variousequivalent modifications can be made without departing from the spiritand scope of the invention, as will be recognized by those skilled inthe relevant art. The teachings provided herein of the invention can beapplied to other haptic systems, not necessarily the exemplary hapticsystem 10 generally described above.

The various embodiments described above can be combined to providefurther embodiments. All of the above U.S. patents, patent applicationsand publications referred to in this specification are incorporated byreference. Aspects of the invention can be modified, if necessary, toemploy systems, circuits and concepts of the various patents,applications and publications to provide yet further embodiments of theinvention.

These and other changes can be made to the invention in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the invention to thespecific embodiments disclosed in the specification and the claims, butshould be construed to include all haptic systems that operate inaccordance with the claims. Accordingly, the invention is not limited bythe disclosure, but instead its scope is to be determined entirely bythe following claims.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, including but not limited to U.S.Pat. No. 5,305,429; Seahak Kim, Masahiro Ishii, Yasuharu Koike, MakotoSato, “Development of Tension Based Haptic Interface with 7 DOF:SPIDAR-G,” ICAT2000, 25-27, Oct., 2000, National Taiwan University,Taiwan; Seahak Kim, Masahiro Ishii, Yasuharu Koike, Makato Sato, “Designof a Tension Based Haptic Interface with 6 DOF,” 4th WorldMulticonference on Systemics, Cybernetics and Informatics (SCI2000) andthe 6th International Conference on Information Systems Analysis andSynthesis (ISAS2000), Orlando, USA, in Jul. 23-26, 2000; Seahak Kim,Masahiro Ishii, Yasuharu Koike, Makoto Sato, “Development of SPIDAR-Gand Possibility of its Application to Virtual Reality,” VRST2000, 22-25,Oct., 2000, Seoul, Korea; Seahak Kim, Masahiro Ishii, Yasuharu Koike,Makoto Sato, “Design of tension based haptic interface: SPIDAR-G,”IMECE2000 (joint with ASME2000), 5-10, Nov., 2000, Orlando, USA; SeahakKim, Masahiro Ishii, Yasuharu Koike, Makoto Sato, “Cutting edge Hapticinterface device: SPIDAR-G,” Proceedings of the 32nd ISR (InternationalSymposium on Robotics), 19-21, Apr., 2001, Seoul, Korea; Seahak Kim,Shoichi Hasegawa, Yasuharu Koike, Makoto Sato, “Tension Based 7 DOFsForce Feedback Device: SPIDAR-G” by the IEEE Computer Society Press inthe proceedings of the IEEE Virtual Reality Conference 2002, 24-28 Mar.2002 in Orlando, Fla.; Seahak Kim, Shouichi Hasegawa, Yasuharu Koike,Makoto Sato, “Tension based 7 DOF Force Feedback Device,” Trans. OnICASE, Vol. 4, No. 1, pp. 8-16, 2002; Seahak Kim, Jeffrey J. Berkley,and Makoto Sato, “A Novel Seven Degree of Freedom Haptic Device forEngineering Design,” Journal of virtual reality, Springer UK (accepted),are incorporated herein by reference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A system comprising: first, second, and third cable control devicescoupled to a support structure and defining a plane, each cable controldevice being configured to pay out and retract cable, and to provide asignal corresponding to a change in length of the cable; an elongatedtool port pivotably coupled at a first end to the support structure andextending toward the plane; and first, second, and third cables coupledat respective first ends to a second end of the tool port, and coupledat respective second ends to a respective one of the first, second, andthird cable control devices.
 2. The system of claim 1 wherein the first,second, and third cable control devices are further configured to applya selectively variable retraction bias to the respective one of thefirst, second, and third cables.
 3. The system of claim 1, furthercomprising a controller configured to determine an angle of rotation ofthe tool port, relative to the plane, based on the signals provided bythe first, second, and third cable control devices.
 4. The system ofclaim 1 wherein the tool port is configured to detect rotation of a toolpositioned therein.
 5. The system of claim 1 wherein the tool port isconfigured to detect translation of a tool positioned therein.